at the edge of...与on the edge of...

at the edge of...与on the edge of...

He is standing at the edge of the cliff.他站在悬崖的边上.强调在某一地点.
There is a knife on the edge of the table .桌边有把小刀.强调在某一平面上.

都有边缘，濒临边缘的意思
on the edge of 已经在边缘上了
at the edge of 濒临边缘，接近边缘